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Math Help - need help with 2 Logarithm problems

  1. #1
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    need help with 2 Logarithm problems

    hey i got a test today and i dont know how to do these 2 problems:

    5^(2x) - 6(5)^x + 5 = 0

    AWNSER: x = 1 or 0

     2log(base4)(x+1) - log(base4)(2x-3) = 2

    AWNSER: x = 28.3 or 1.7
    Last edited by Sonx; December 2nd 2008 at 06:10 AM.
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  2. #2
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    Hello, Sonx!

    5^{2x} - 6\!\cdot\!5^x + 5 \:=\: 0
    That ugly expression is a quadratic.

    It factors! . . (5^x - 1)(5^x-5) \:=\:0


    So we have: . \begin{array}{ccccc}5^x-1\:=\:0 & \Rightarrow & 5^x\:=\:1 &\Rightarrow& \boxed{x \:=\:0} \\ \\[-3mm]<br />
5^x-5\:=\:0 &\Rightarrow&5^x\:=\:5 &\Rightarrow &\boxed{ x \:=\:1} \end{array}




     2\log_4(x+1) - \log_4(2x-3) \:= \:2

    We have: . \log_4(x+1)^2 - \log_4(2x-3) \:=\:2 \quad\Rightarrow\quad \log_4\left[\frac{(x+1)^2}{2x-3}\right] \;=\;2

    . . . \frac{(x+1)^2}{2x-3} \:=\:4^2 \quad\Rightarrow\quad (x+1)^2 \:=\:16(2x-3)


    . . . x^2+2x+1 \:=\:32x - 48 \quad\Rightarrow\quad x^2-30x + 49 \:=\:0


    Quadratic Formula: . x \;=\;\frac{\text{-}(\text{-}30) \pm\sqrt{(\text{-}30)^2 - 4(1)(49)}}{2(1)} \;=\;\frac{30 \pm\sqrt{704}}{2} \;=\;15 \pm4\sqrt{11}


    Answers: . x \;=\;\begin{Bmatrix}15 + 4\sqrt{11} &=& 28.26649916 \\  \\[-4mm]15 - 4\sqrt{11} &=& 1.733500839 \end{Bmatrix}

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